System of telephony



(No Model.)

B. THOMSON. SYSTEM OF TELEPHONY. No. 481,878. Patented Aug. 30, 1892.

- Telephony, of which STATES ATENT Prion.

'ELIHU THOMSON, OF sWAMPsco'rT, MASSACHUSETTS.

SYSTEM OF TELEPHONY.

SPECIFICATIOiN forming part of Letters Patent No. 481,878, dated August 30, 1892. I Application filed February 15. 1892- $erial No. 421,511. (No model.)

To all whom, it may concern:

Be it known that I, ELIHU THOMSON, a citizen of the United States, and a resident of Swampscott, in the county of Essex and Commonwealth of Massachusetts, have invented a new and useful Improvement in Systems of the following is a specification.

The presentinvention relates to atelephonic system in which an alternating current ofsuch low rate of alternation as not seriously to interfere with speech is used upon the line for transmission in place of a continuous current or battery-current and the invention is applicable to telephonic-exchange work, whereby an alternating current generator may be placed at an exchange or station to which a large number of subscribers lines pass, which alternating-current generator may be a dynamo driven at the requisite speed to produce the alternations required. These alternations are divided or induced into the subscribers lines and form the means for transmission from the subscribers lines toother s cribers lines, to time being be connected through the exchange or otherwise. The preferred rate of alternations is low, and as low as thirty-two vibrations per second, or even below sixteen vibrations per second are available. These rates of vibration or alternation are so low that although the instruments are subjected to them they do not seriously interfere with speech; as the tone they produce is almost-inaudible on account .of the small volume of air set in motion by the diaphragms of the instruments. In my system there is dispensed with all local batteries at the subscribers end of theline, and the system is, as it were, a closed-circuit system possessing great flexibility. The system also permits the working of theannunciators at the exchange by the subscriber inomentarily opening the line by a switch, or

better, by the simple act of lifting the telephone from the hook, while the replacing of the telephone on the hook again signals the exchange that the use of the line is discontinned. The system also provides circuits, if found desirable, so that thereshall notbe any circuits actually grounded, as connections to earth through condensers-maybe.

made instead of returning through a continu- Which they may for the and the secondarycoils I ous conductor or a metallic circuit connected to earth, suoh as is ordinarily employed.

The invention will be understood by reference to the accompanying. figures.

Figure 1 is a diagram illustrating the invention as applied to the exchange or conral station of atelephone system to which the subscribers lines are; led. Fig. 2 shows the preferred character'of current used in operating my system. Figs'g;-..3i;and at are diagrams showing the arrangement at the subscribers end of the system. Fig. 5 is a moditied type of transmitter, which may be employed in some cases. Fig. 6 shows a preferred arrangement of circuit, which maybe used in connection with the system.

In Fig. 1, at G, is indicated a generator of alternating currents, which may consist simply of a coil of wire wound upon a laminated iron core and which is driven by suitable power, or, preferably, around which is driven a set of magnets N S. The generator A has a coil in which alternating currents are genera-ted, and the preferred form of Wave is indicated in Fig.'2-something like asawtooth or pointed Wave. The construction of the field and armature will require to be-moditied to approximate this form. of Wave. These are principles now well understood in the art and the result may be achieved in a number of different ways. Connections are led from the coil A. in which the alternating currents are generated, to a set of secondary coils or transformers, (indicated at B B B B as manyv as there are subscribers lines entering the exchange. These transformers may be connected in multiple or series orin anyother arrangement, but are shown connected in multiple from the terminals leadingf-rom the coil A. The primary coils, therefore, receive the same alternating-current impulses or pul' satingimpulses asare generated inthecoil 7 These primary coils work inductively on secondary .coils wound upon the same core or in inductive relation to theprimary coils,

arein the subscribarranged to be in thesubscribers lines when communication is desired to be had. The subscribers lines leading from these secondaries are shown as four in numbers/b 0 cl and may,as usual, he led off to considerable distances. The terminals of the ers lines or secondary coils not connected. to the lines a b c d are arranged to be connected to earth at E through a condenser K or directly to earth, as desired, and in the lines a b c d, as at e f g h, are arranged annunciators, which so long as current flows in the lines retain their drops in position, but on a momentary interruption of drops to fall and indicate that thesubscriber desires to use the line or call the exchange. Arrangements should exist, but they are not shown in the figure, for plugging into the subscribers lines, as usual, the exchange-instruments, whereby the operator can communicate with the subscriber. The transmitter and receiver used in the exchange will be similar in pattern -to that which the subscriber uses. on a call being indicated by the dropping of an annunciator, say at e, the operator plugs or switches line b in the ordinary way to the other subscriber's line, and at the same time disconnects the earth at E. his may be done by the insertion of plugswitches or by the ordinary exchange-switchboards. Assuming then that the lines a b c d have been connected through the exchange in response to a call from either I) or a, communication can now be had between the subscribers on those lines.

In Figs. 3 and 4: is shown the subscribers equipment, which consists of a call-bell H, consisting of an electro-magnetic arrangeinent responsive to an alternating current of low frequency and considerable intensity. It also consists of the transmitter-transformer t, a coil of which, linewhen in use, while the secondary S is connected locally through the transmitter T, whereby variations of the amount of closure of the circuit through the coil S may be obtained, and the secondary S may have a current of very low potential when metallic electrodes are used in the transmitter orvwhen the variations of resistance in that circuit are obtained by a diaphragm acting on a mercury globule. It would be of higher resistance, but still of comparatively coarse wire if a carbon transmitter were used, and in the case of a static transmitter, such as is shown in Fig. 5, consisting of a condenser whose nlates are brought near together and capable of being moved by the waves of sound of the voice it would be a very high resistance-coil of very many turns. R represents the receiver, introduced into the line in series with the coil P, and they may be connected through the transmitter, and

a transformer, as is wound accordingly. The receiver is of the ordinary type, such as is used in common telephone practice, consisting of a magnetized core or a fine soft-iron core, subjected to the action of thecoil through which thelinecurrents flow, with a diaphragm in front of the end of the core for receiving the vibratory action and translating them into corre: sponding sound-waves. An earth connection should be made, as at E This earth con current occurring, allow their is a momentary opening of the line.

as P, is connected into the nection may, however, not be a complete conducting connection,but may be made-through a condenser of suitable capacity, so that the line remains insulated while still capable of transmitting the waves of current. At R is shown in dotted lines the position of the telephone-receiver when hung upon its supporting-hook or rather its position in the act of being hung upon its hook. WVhen unhung, contact 71 is closed and would form, if it is desired to use the connection, a shunt to the bell-magnet H. As, however, the bell-magnet does not respond to the normal impulses during speech, it is not necessary to so connect it except to avoid the self induction or resistance. At j k are contacts, which are operated as follows: When the telephone-1e ceiver R is unhnng, the circuit is closed atK by the movable lever on which the telephone is supported, (indicated at Z,) always tending upward and depressed during the hanging of the telephone-receiver. This completes the line through to the transmitting-instruments. When the receiver R is hung on the lever Z, contact is closed at j and the connection is made which cuts out the transmitter and receiver and keeps only the bell H in the subscribers line b. This set of switching actions is not essential to the operation of the system, as is manifest, but I find it is quite useful in the following particular: In taking the receiver R from the hook, contact at j is opened before contact Z0 is closed, or, in other words, there This momentary opening of the line maybe the means of signaling to the exchange or dropping the exchange-annunciator, the system operating like a closed-circuit system. When the annunciator-drop is lifted, itis held in its lifted position so long as the line from earth plate E to earth E is intact, whether the condensers are used in the line or not. During this time the secondary B is sending impulses at a low rate-say sixteen or twenty'vibrations per second but not of suificient force or potential to ring the bell H. The lifting of the receiver R and lever 7. opens contact j a slight time before closing it at It, and the annunciator 6 drops, indicating that the subscriber has lifted the telephone from the hook and desires to communicate. The exchange now answers the call by plugging-in the telephone at the exchange, using a telephone set similar to that which the subscriber has. The subscriber speaking into the transmitter T varies in any suitable manner the resistance in the circuit S, which is in inductive relation to the coil P in the line. The circuit of the transmitter S forms a closed circuit secondary to the primary coilP in the line through which alternating currents are constantly flowing when such coil is in circuit. The variations of resistance of this closed secondary circuit set up variations of counter electro-motive force in the coiLP, which react throughout the connected lines and at a rate corresponding with speech-vibrations, and

IIO

impulses are'carried to the other subscriber on the line at c, where they may be heard in receiver R 'if lifted from the hook, as at 1*,

whereby contact 10 is closed.

are substantially the same. It may be mentioned that the back contact'of the lever Z, (indicated at ji) may either be connected to earth directly, or it may be connected by a Wire to earth, as shown in dotted lines 10, instead of the earth connection to the line leading through the instruments. In this case the earth-plate to the left in the figure will be dispensed with and the earth-plate to the right will be connected by the wire to through the instruments to the left-hand contactatj.

Since alternating currents or impulses flow equally in both lines bandcwhen connected, speech may be had back and forth from one end to the other by the use of the transmit ters and receivers provided, and although there is an alternatingcurrent traversing the line simultaneously it is a low-period current'which hardly produces any effect in the receiver on account of its low rate, and in fact in any case could only produce a very low hum upon which the waves of the voice are superimposed.

With the form of wave shown in Fig. 2, in which there is a quick change of the current at all times, there are no dead-points of com munication which would stop the action of the transmitter except at: the tops of the waves; but these'areso small aportion of the general wave that they do not, affect the speech transmission perceptibly.

It remains to describe the arrangement by which the exchange calls the subscriber. For this purpose a transformer, as at B, may be provided, which is capable of being connected into the subscribers lines by proper switch appliances, as at V, and which transformer B may be made to produce currents of great vigor which add themselves to the currents already found upon the lines and due to the transformers B, B B and B With this added current the bell-magnets H may easily be made to respond to .the alternations, their adjustment being such that during the transmission of speech-alternations they are incapable of operating the bell and require the added current to actuate them. The rate of alternations impressed upon the lines may be just rapid enough to produce a low hum and may serve, therefore, as an indication of the condition of the line; If the subscriber in listening at his receiver does not detect the low hum he will knowat once that the line is interrupted. If, however, it be heard-with the normal strength and rate it is an indication that the line is complete.

In-my system the subscribers apparatus a fixed-apparatus not re-;, quiringi attention such as is demanded in the becomespractically *Thesubscriber 1 on the line 0 has'a similar set of instruments to thosejust described,and the connections replacing of the same,

. be replaced by the keeping up,of a battery, and the electrical i energy which is at the command of the subscriber is as unlimited as-the resources of the exchange permit. If it is desired, no part of the system need be grounded.

Fig. 5 shows a transmitterin'which the secondary S is of very fine wire and connected to two parallel plates which form a transmit-v ter condenser, the movements to and front the plates during speechvaryi ng the condens ing capacity, and therefore the amount of flow of currentin S and inductively the action of the coil P. This arrangement to be effective should have as much condenser surface aspossibleor a higher rate of alternations be used than with the other type of transmi-tter.

It is an improvementin the operation of my system to introduce a condenser of moderate capacity in of thetransformers B B"B B of these condensers should be so small that no interference is produced with the opera tion of the transformer, or, inother Words, they do not'short-circuit the secondary of the same; but that for quick impulses they shall practically bea shunt around the secondary of the transformer B. The waves of speech may pass through the condenser, Fig, .6, with perfect freedom, whereas the alternating waves supplied to the line would not find sufficient capacity in the condenser to be much affected thereby: .In this way the self-induction of the secondaries of the transformers may be in a large measure eliminated.

- In order to insure that the circuit of each The capacity subscribers line shall be opened for a moment the receiver and the it is advisable to provide the sustaining hooks orleve'rs with dashpots or other retarding an appreciable interval elapses in the change of position of the lever from its upwardto it's downward position or the reverse. Such devices are indicated at D D as dash-pots filled with fluid for checking themotion. Of course it is not essential that in signaling from the exchange outward to the lines that the same during the removal of frequency of alternations be used, or that alternating currents be employed at all, as by making the subscribers bell sensitive to in:

terrupt-ed currents, or by making them sensitive to particular periodsv of currents the sig-' nals may be effected by different currents from those which are used normally upon the line. The signal arrangements do not form an essential feature of the invention, and may ordinary magneto and a proper signaling system used in connection therewith; but it is preferred to combine the features which have been. described in the complete system of this character, as it gives etlzonomy of operation and economy in the p ant.

What I claim as my invention is I 1. In a system of telephonic transmission,

.a generator of altern atiug or varying currents a shuntaround the secondary coil mechanism, wherebytransmitters responsive of little or no audible eifectin the receivinginstrunicnts, inductive devices or inductioncoils operated by said currents whereby similar induced currents are supplied to the separate lines, means, such as switches, for connecting such separate lines, receivers in the said lines, and transmitters also in said lines having inductive coils, one in the line and one in a local circuit, including a resistancevarying or current-varyin g device responsive to sound-waves.

2. In a system of telephonic transmission, a set of transformers or inductive devices the primaries of which are fed by alternating or varying currents of low period and the secondaries of which are connected into the circuit upon which speech is to be conveyed, receivers in said lines, devices orinductioncoils with primaries connected to line, and secondaries connected to currentvarying to sound-waves. 3. In a system of telephonic transmission,

a set of transformers or inductivegdevices the I primaries of which are fed by alternating or varying currents of low period and the secondaries of which are to be connected into the circuit upon which speech is to be conveyed, condensers in shunt relation to such secondaries, receivers in said lines, devices or induction-coils with primaries connected to line, and secondaries connected to current,- varying devices or transmitters responsive to sound-waves. a

4.. In a system of telephonic transmission comprising a number of lines, means for generating and transmitting alternating or varying current impulses of comparatively low period through the lines, and means for modifying such waves of current, consisting of an induction-coil one of the coils of which is in the line and the other of which is in a local circuit including the transmitter, substantially as described.

5. In a system of telephonic transmission comprising a system of lines normally fed by alternating or varying impulses of currents, signaling devices in said lines responsive to callingcurrents and unresponsive to the normal pulsations or alternations, telephone-receivers for said lines, and transmitting mechanism consisting of a line-coil in inductive relation to a local coil, in the circuit of which latter is placed a current-varying device, such as a variable resistance, said cum'ent-varying device or transmitter beingresponsive to vocal or other sounds.

(i. In a system of telephonic transmission, a system of lines normally fed by alternating or varying impulses of current, signaling devices in said lines responsive to calling-eurrents, switch stations or exchanges, annunciators at said stations individually responsive to the opening of their respective lines, receivers adapted to be connected into said lines by the operation of suitable switch mechanism, and transmitters likewise adapted to be connected to such lines, said transmitters having a local circuit including a resistance or current-varying device responsive to sounds, said local circuit being in inductive relation to a coil in the line-circuit while the transmitter is in use.

7. In a telephone system, a line or circuit connecting the exchange with a subscribers station and normally on closed circuit, a generator for feeding to said current alternating or varying impulses of current suitable for the operation of transmitters, a signal device at the subscribers end of the line unresponsive to the alternating or varying current which operates the transmitters, butresponsive to special calling-currents, and an an-nunc'iator at the exchange operative upon the opening of said circuit.

8. In a closed-eircuit system of telephonic transmission, lines on closed circuit orthrough condensers, means in each of said lines for generating or conveying to it alternating or varying impulses of current of low period, transmitters and mechanism for keeping said transmitters in circuit in said lines when in use, comprising a coil in the line with alocal coil in inductive relation thereto, and resistance or current-varying devices responsive to vocal or other sounds.

9. A telephone-exchange system comprising a generator of alternating-current impulses, means for conveying individually such impulses of varying current to the individual lines leading from the exchange, annunciators or signal devices in said lines, signal apparatus in said lines at the subscribers or users part of the line responsive to currents sent out from the exchange, switching devices for interconnecting the lines at the exchange, transmitters and receivers connected into the lines when in use, said transmitters consisting substantially of induction-coils, one coil being in the line and another in inductive relation thereto when connected to mechanism for varying current or resistance in the circuit of said coil in correspondence with sound-waves reaching the transmitter.

Signed at Lynn,-Massachusetts, February 12, 1892.

ELIHU THOMSON.

Witnesses:

J OHN W. GIBBONEY, BENJAMIN B. HULL.

' It is hereby certified that in LetterS'Petent N 0. 481,878, greeted August 30, l892,

upo the application of Elihu Thomson, of Swainpscob, Messachus'etts, for an improve ment in Systemsbf Telephony, an error appears in the printed epecifi'cationiequii' ing the followii g cor eciion, 'viz.: 1n 1ii1e'76, page 4, the word cl rrent should read circuit and than'the said Letters Patent; should be read with this correction therein thatthe same may ed iform to the record bf the case in the Patent Oifice. Q

Signed, eountersigned, afid sealed this 4th day of Octobei', A. D; 1892.

' I CYRUS BUSSEY,v

Assist/amt Secretary of the Interior.

[SEAL] Countersigned W. E. smoiws,

flommz'ss'ionerof Patents; 

